At present in order to manufacture a large-diameter fuselage section made of laminated composite materials, fibre strips preimpregnated with resin, such as carbon fibres with epoxy resins and graphite with bismaleimide resin, are used. The composite strips are placed automatically by means of one or more supply heads of a special machine on the outer surface of a mandrel having the form of a solid of rotation about a given axis. The supply heads of the machine and the mandrel are moved relative to each other so that the heads apply the strip onto the mandrel following a relative translatory and rotational movement with respect to the axis of the mandrel. The skin of a fuselage section consisting of a composite laminate is thus formed on the outer surface of the mandrel. The whole assembly is then surrounded by a vacuum bag and subjected to a single polymerization cycle inside an autoclave.
Deposition of the vacuum bag constitutes a critical phase in the production process owing to the fact that the bag material is delicate per se and, since it is very big in order to cover a large-size body, there is a considerable risk of it being damaged both during application and during the previous movement and handling stages. A standard vacuum bag used for polymerization of a fuselage section is composed of three separate sheets which are placed in succession on top of one another. A first sheet, consisting of a separating film, is placed in contact with the composite material to be polymerized. A second, porous, so-called breather sheet is arranged in between the film and a third impermeable sheet, generally made of nylon.
Hitherto, in order to apply the vacuum bag onto the fuselage section to be polymerized, the methods which have been employed are such that they result in considerable logistic difficulties as regards handling of the bag material or do not allow precise positioning of the bag. In some cases the bag is lowered from above onto the mandrel using two bridge cranes. In other cases the bag material is pulled and extended manually over the mandrel by operators transported on cage elevators. Often the two end portions of the vacuum bag are joined together manually by an operator who must lie flat on the ground underneath the mandrel.